1. Field of the Invention
This invention relates to a method for treating stainless steel disc drive components to increase torque retention and plate stiffness properties.
2. Description of the Prior Art
An important form of data storage and retrieval involves the use of disc drives comprising circular discs coated with a magnetic or reflective medium which are rotated at high speeds proximate highly sensitive sensing mechanisms. These mechanisms, commonly referred to as read/write heads are pivotally connected to mechanical actuators and swept across the surface of the discs to "write" or "read" data therefrom. Connecting the heads to the actuators is a series of fixedly interconnected components which extend across the face of such discs to bring such heads proximate any data retaining area of the rotating disc. Such components include an actuator member having one end pivotally mounted to the actuator with the other end terminated by an "E-beam" which supports a "load beam" laterally extending therefrom and frictionally fastened thereto in a stacked vertical relationship by a component commonly referred to as a swage mount. With disc drive access times decreasing below the ten millisecond threshold, such interconnected components sweep across such discs at rates sufficient to generate acceleration levels up to 40 Gs. Therefore, fabrication methods to make frictional fasteners capable of withstanding such forces are critical to successful operation of these types of data storage systems.
Swage mounts used in conventional disc drive applications are intricately formed stainless steel fasteners designed to secure disc drive load beams to respective actuator members and prevent relative rotational movement therebetween. Having thin rectangular bases with upturned circular hubs, the mounts typically engage a complementally formed aperture in the load beam after being affixed to an E-beam. Upon engaging the load beam aperture, the swage mount hub is slightly deformed outwardly, against the load beam wall defining the aperture, forming a tight frictional bond. The efficiency of such a bond is commonly referred to as "torque retention" and depends not only on the inherent frictional characteristics of the metal but also on the mass of the hub.
Under current practice, torque retention is maximized by increasing the coefficient of friction of the stainless steel using an annealing process which hardens the component to a predetermined durometer magnitude. The process involves exposing the material to a constant elevated temperature in excess of 1800 degrees F., known as the "red area" for stainless steel because of the fiery red hot color apparent therein. Once the component is sufficiently heated, it is subjected to a furnace cool which involves linearly ramping the temperature downwardly until conditions approaching ambient are achieved. A serious disadvantage to treating swage mounts using this process is that the maximum achievable frictional properties of the treated swage mount material sets a lower limit on hub heights, thus preventing further miniaturization of the components using currently established assembly techniques for disc drives. With market emphasis placed on smaller and smaller disc drive assemblies, component fabrication techniques enabling decreased stacking heights of components such as swage mounts are critical. An industry indicia, commonly known as a "form factor," measures the relative stacking heights of such components to predict subsequent overall sizes of such disc drive top assemblies. As a general rule, the lower the form factor, the more desirable the product.
Another problem inherent in the current practice of treating swage mounts involves the inducement of high frequency resonances. Swaging of the swage mount to the load beam causes distortion of the swage mount plate along with an uneven gram loading against the periphery of the swage mount hub. As a result, high frequency resonances during operation of the disc drive are induced, often causing perturbations in the accessing or writing of data to the disc.
What has been needed, and heretofore unavailable, is a process by which miniaturized stainless steel swage mounts can be thermally conditioned into a torque retaining fastener for disc drive load beams with increased plate stiffness to minimize high frequency resonances during operation. The method of the present invention satisfies these needs.